Certain devices such as wafer defect scanners, laser printers, document scanners, projectors and the like employ a collimated laser beam that scans across a flat surface in a straight line or curved path. These devices employ tilting mirrors to deflect the beam to perform the scanning. These tilting mirrors may be, or may include, Micro Electro Mechanical Systems (“MEMS”) devices. The actuation of mirrors used in MEMS devices, referred to herein as MEMS mirrors, can be via the electromagnetic, electrostatic, piezoelectric, and thermoelectric effects, depending on application.
One type of common MEMS mirror includes a stator and a rotor, with the rotor or structures carried by the rotor being reflective. The stator and/or rotor are driven with a drive signal which results in the rotor oscillating with respect to the stator, thereby changing the angle of reflectance of an incident light beam on the rotor. By oscillating the rotor between two orientations, an opening angle of the mirror is defined, and scanning of the light beam across the flat surface is accomplished.
When a device employing such a MEMS mirror, which is actuated in its self-resonance, is switched on, the MEMS mirror begins an initialization or startup period during which it goes from rest to a oscillating at a resonant frequency and with a desired opening angle. So as to enable full performance of such devices as quickly as possible, it is desirable for this initialization period to be minimized. Conventional MEMS mirrors are simply driven with a constant amplitude drive signal in both an initialization mode and a normal operation mode, which may provide for a longer initialization period than desired. Therefore, further development into techniques for reducing the initialization period of a resonating MEMS mirror is needed.